Featured The Differential Between You and Me

Discussion in 'Motorsports' started by leon_90, Jan 19, 2019.

  1. leon_90

    leon_90
    Columnist for RaceDepartment Staff Premium

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    Diff_Audi.jpg

    How do you prefer yours?


    Differential, the trickiest thing to get right in your setup. There’s who prefer it to be more open, less open, locked, making the car more oversteering, less oversteering, understeering, balanced, neutral. Who goes for better acceleration, who likes to have a more agile turn in and cornering. Then there is the need to adapt to different solutions like FWD, AWD and 4WD, or different racing surfaces, for rallying. It really is a difficult subject, and one that would require taking into consideration an infinite number of combinations and possibilities.

    However, one thing is for certain, each (sim)racing driver has his own philosophy when it comes to tweaking the differential, and we thought it could be interesting to open up a container where to share all these stimulating ideas. Obviously, it is impossible to conclude which is the best configuration for your differential, because there simply isn’t any, being very much dependant on the driving style and the car driven. Still, a healthy discussion about which might work best for what and when might be a fascinating read. Moreover, if you happen to do track days or real racing, it would be interesting if you could share your experience, and eventual differences between setting up your diff in a sim and in an actual sports vehicle.

    Let’s hear your thoughts about it!


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    Last edited: Jan 19, 2019
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  2. Snailer

    Snailer

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    No differential is best differential.

    Quad motor AWD torque vectoring is where it's at :D
     
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  3. apex11

    apex11

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    Limited slip diff................... always makes me laugh when people talk about Traction control and arcade etc.... LSD is traction control...
     
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  4. BrunoB

    BrunoB

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    I have probably a special use of diff settings in a racing game.:ninja:
    Because I have to use a wheel with handcontrolled brake/throttle(leg issue) Im unable to turn the wheel more than about +-30 degree.
    Otherwise the fingers get too twisted for any fine control.
    OK that means that to get the car to turn enought in tight corners I have to use an abrubt downshift in the corner entry together with an extreme diff coast setting(oooversteer) to get the car to rotate - at all.:rolleyes:

    So Im pretty dependent of how realistic the game is able to simulate the diffs behaviour.

    Hehe that was one of the reasons I stopped my iRacing membership because one of the devs overnight introduced an automatic downshift prevention on (among others) my prefered car the Lotus 79.:poop:
    It became suddenly impossible to get the car to rotate for me.
    Haha automatic downshift prevention on the ooold Lotus 79.:mad:
    Very realistic iRacing.
     
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  5. Richard Wilks

    Richard Wilks

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    The Diff, got wrong by Devs and Modders ever since the GPL days...
     
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  6. RaceNut

    RaceNut

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    It's not only the "Diff" that may not be properly modeled but, the entire drive-train behavior. Few titles go to any length to provide much - if any, advanced physics modeling that includes gear-lash and component flex variables. I think iRacing has the best example of such effects and it can be seen, heard (Engine Load & Surge) and felt (motion). RaceRoom has it too but, seems a bit less dynamic to me in how it reacts to bumps and rumble-strips.
     
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  7. Sky

    Sky

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    i prefer one that i don't have to touch
     
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  8. silhouette106

    silhouette106

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    I find setting up a diff. relativly easy:

    Car want to an impression of a spinning top when i touch the accelarator: Lower Power
    Car plows like a tractor on exit: Higher Power
    Car doesnt want to do corners: Lower Coast
    Car want to jump apex kerbs like a steeplechase: Higher Coast
    (though you always gotta tighten the nut behind the wheel before you do any setup work!)

    Still got get my head round what preload does to the car.
    As well as what the numbers actually translate to 'gear-wise' in the diff.
     
    Last edited: Jan 20, 2019
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  9. Nick Gregory

    Nick Gregory
    Forever a backmarker Premium

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    You know you're a car guy when you say "did you try the LSD?" and don't thing anything else of it.
     
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  10. MotherDawg

    MotherDawg

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    Diff... the line is:
    https://www.taylor-race.com/sites/default/files/DIFFERENTIAL ESSAY W PHOTOS2.pdf

    My own trek is (repost) :

    You're doing it all wrong! :D

    If one mashes up the "Loud Pedal" coming out of a tight corner, what ever the diff settings, if the rears light up, none of it matters.

    "By limiting the slippage between the rear wheels, the differential can have a profound impact on the car's handling. The rule of thumb is: the more the diff limits slippage, the more the car will tend to go straight or understeer -- up to a point. On the power side, if enough torque is applied to spin both wheels, the car will snap into oversteer." -- http://www.intothered.dk/simracing/differential.html

    That mean, on a long fast sweeper, at 100% lock, the inside want to rotate at the same speed as the outside. The rear axle wants the car to go straight. 100% lock, the car will not turn. At 0% lock, it will turn all we want but it wont accelerate out of anywhere (smoke show?). Just one more balancing act !

    So if the car wants to over rotate when you touch the accelerator: Augment Power...
    If the car does not to want to rotate during exit: Reduce Power.

    Setting lock percentage by how the rear end pops out is not good. Wrong driving style. IRL, bye bye rear tyres in just a few laps. Always set your diff while driving with your head... not sliding, all wheels well planted.

    To finish, there are a lot of very technical books out there but, for many readers, going through those can be quite harsh. Many years ago, I learned a lot from a little book that was a breeze to read: Four Wheel Drift by Steve Smith. The guide that came with Grand Prix Legend. The people who did not go through it found GPL undrivable. The racers who did... learned to drive.

    Exert: "Alison Hine uses the tire temps to help adjust the differential. Taking a reading coming off the Parabolica where you’re most likely to get wheel spin, she looks at the temp of the inside (RR) tire. If it’s higher than the outside tire temp, which would normally be the hotter of the two, she knows she’s spinning the inside tire, and adds a clutch or two until the temp drops. She knows she’s gone too far when both tires break loose together, sending the car into snap oversteer. Then she removes one clutch the inside tire should now begin to spin just before the outside tire breaks loose."

    In Grand Prix Legend:
    --- High ramp angles equal Low locking %
    --- high clutch # roughly equals to high preload %

    Augmenting preload "mainly" sets the minimum level of locking so you don't get an open diff during the transition between power and coast. Adding clutches Modifies how fast that transition, the locking, happens. So during mid corner, applying-lifting-applying, if you're fighting the car, it's unstable, augment preload. I haven't played enough with clutch numbers to know what it really does


    Gilles
    *** Open mouth - insert foot - echo Internationally ***

    ---
    How can you "Disagree" when this is how it is... I haven't invented anything here.
    ^^^^
     
    Last edited: Jan 19, 2019
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  11. Trebucht

    Trebucht

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    I'm glad you're bringing this topic up. There are many misconceptions about what a diff does, what a certain percentage of lock means in terms of actual physics and what effects can be obtained by the correct usage of locking. The term 'oversteer/understeer' comes to mind, although the purpose of diff settings in a race car don't necessarily have much to do with that. I myself have real life experience as well as a ton of AC testing behind me regarding the 'universe of differentials'. Explaining everything in detail will take a moment, maybe I can file a litte diff-guide in the future.
     
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  12. MotherDawg

    MotherDawg

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    ...you on dope? :O_o:

    The Mechanical Limited-Slip Differential Revisited: High-Performance and Racing Car Application.
    International Journal of Applied Engineering Research ISSN 0973-4562 Volume 13, Number 2 (2018) Department of Industrial and Mechanical Engineering, Automotive Group, University of Brescia, Italy.
    https://www.ripublication.com/ijaer18/ijaerv13n2_89.pdf

    And many other books, documents and thesis that say otherwise...
     
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  13. Durge Driven

    Durge Driven

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    Exactly, pity studios can not get on the same page and develop 1 engine for us

    All debate and negativity from 10 engines would turn into constructive feedback ( good or bad ) for 1 engine

    Tell me why that would not be better ?
     
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  14. michelforest

    michelforest

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    I have a confession to make: setting up the car is my least favorite aspect of simracing... I love to drive, but if I was a multi-millionaire, I would hire my own personal engineer to set up the car to my preferences... (He wrote, bowing his head in shame... ;))
     
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  15. Trebucht

    Trebucht

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    "On high-performance vehicle applications with a high power-to-weight ratio it can also help to improve cornering behaviour and stability through the development of a yaw torque with a direct impact on handling characteristics" - https://www.ripublication.com/ijaer18/ijaerv13n2_89.pdf --> yaw torque as in rotation.
    The behavior of a car in terms of over-understeer is partly influenced by the diff settings. All the other suspension components can out weight the impact on over-understeer to a point where the diff settings (almost) don't matter any more. It's job is to help with rotation through fast turns, give traction out of slow turns and stabilize when braking/coasting. All that after the suspension setup deals with over-understeer. Its a fine act of balance, but the diff shouldn't be the main influencer. Otherwise the suspension isn't working to its max potential => possible time loss.

    You are right in the way that when we try to describe how a diff actually works we like to use 'over-understeer' to help understand its purpose.

    What I like to do (very brief overview) : start with about 50/50 lock (power/coast in %) and get the suspension right. Making sure all the dampers work correctly, spring rates are set for the car/track combination, arb are in a good balance and so on. I then try to tweak the diff, usually resulting in more % for both power & coast. I then repeate the process multiple times. Susp - diff - susp - diff...where the diff is at the tip of the scale, always making sure the suspension can do its job to the full potential.
     
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  16. Kyuubeey

    Kyuubeey

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    It depends on the power level, drivetrain and driving condition. Generally I follow the rule of keeping both directions as open as possible, and I like a bit of preload.

    For a race, I'll lock both directions more for stability. For a fast lap, especially in a downforce car in a fast track, I'll set the settings lower as to not bog the engine in high G turns.

    If I'm driving FWD however, completely open coast and very close to fully locked power. Always been fastest to me. In a driftcar and in some cases rallycar, very close to or fully locked both directions, maxed out preload, so on. In a driftcar especially I want the rears to spin as consistently to eachothers' speed as possible: for consistency, not necessarily performance.
     
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  17. UnixRoot

    UnixRoot

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    Diferentials are for kids. ;)

    Try some cars with locked/welded diff or no diferentials at all, like the Porsche 917k or 935.

    It's fun to ride a cannonball on knifes edge. Always struggling between understeering and oversteering, depending on you throttle control.
     
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  18. MarkR

    MarkR

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    For me in the real world of track cars I find adjustable suspension, tyre choice, good reliable braking and sometimes an ecu map far more important than the differential. Sure I want the car to have a good differential(s) but only the cars with electronic systems have ever had the ability to adjust them in my experience.

    The endless settings available in sims and racing games is where they differ most from real life track cars for me. Sure the very top of motorsport may have this level of adjustability and teams of engineers to set them up properly, track the data, run the hundreds of laps and simulations required to know if it's faster.

    For front wheel drive the VAQ differential on my daily driver Cupra is a good compromise, in comfort mode for road driving the differential effect is mild and unobtrusive. At the highest Cupra setting, paired with Michelin Pilot Sport Cup 2 tyres it'll cling to the apex on track in a way that takes some getting used to. It'll even leave a set of 11's on the tarmac in the tighter corners - crazy for a FWD car. It helps that the damper stiffness can also be adjusted with the diff because they all need to work together to be effective imo. As technology that enables cars to work on the road without being overly harsh and still fun on track it's a decent compromise (anyone who's driven a fidgety Audi RS car on standard dampers will know how annoying that can be). It still in't as good as a specific track car like my Megane R26.R and that has almost no adjustability at all. Superb front suspension setup and diff work together in perfect harmony though, hit the apex and the throttle just pulls the car around.

    The centre differential adjustment on the Impreza was fun too, but more of a gimmick than really impacting the performance that much. It was fun to move the power rearwards on an empty, damp Pembrey trackday and slide about for a lap or two. Again adjustable suspension to be able to soften for the bumps or wet conditions on the track made far more difference imo. The Evo 8 MR had no driver adjustment but the active yaw control in that car was incredible, it could make almost anyone look like a driving god.

    None of the lightweights Westfield's, Caterhams, Atom etc have - to my knowledge - had any differential adjustment but they all worked superbly. The ability to adjust the ride height and damper stiffness and tyre pressures - manually - is by far the best way to change real car behaviour imo.

    So that's my take on differentials froma trackday enthusiasts perspective. It's good to be able to adjust them in games but I don't think it's the height of realism for anything other than the most elite motorsports (even then I believe many racing series prevent this to keep costs down.)
     
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  19. Dirk Steffen

    Dirk Steffen
    Porsche Factory Jackass™ Premium

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    Differential who?

    [​IMG]
     
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  20. apex11

    apex11

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    To the person that disagreed with me:

    "Powerful rear-drive cars from the sixties often had a primitive form of traction control called a limited slip rear differential. Sometimes referred to asPositraction, a limited-slip rear axle will mechanically transfer power to the rear wheel with the most traction, helping to reduce, but not eliminate wheel spin."

    LSD is a driver aid and no longer 'primitive' form of TC....
    Just ask Quaife.....they make a buck from them... unless you saying LSD do nothing?
     
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